This invention relates to ring laser gyros, and more particularly to a detection system for such a laser gyro which provides signals representing the fringe pattern and signal intensity from the same detector array.
In ring laser gyros, generally photo detectors, such as photo-diodes, are placed either directly on one of the gyro mirrors or at some other position where they can receive optical signals from both the clockwise and counter-clockwise rotating beams of the laser. Typically in prior art systems, two pairs of such photo detectors are used to generate quadrature related signals which can be compared with each other in appropriate computation circuitry to determine magnitude and direction of the input velocity to the gyro. Typical such prior art systems are disclosed in U.S. Pat. No. 3,721,497, issued Mar. 20, 1973, to Sidney G. Shutt et al., assigned to the assignee of the present application; U.S. Pat. No. 3,468,608, issued Sept. 23, 1969, to B. Doyle; and U.S. Pat. No. 3,854,819, issued Dec. 17, 1974, to Andringa.
While none of the aforementioned patents have any disclosure in this regard, in more recent systems, it has been found highly desirable to generate a signal in accordance with the intensity of the fringe pattern signal. This is to provide a control signal for tuning and adjusting the laser for maximum output. For such an intensity signal to be useful, it must be fairly constant in value, i.e., the fluctuations in the fringe pattern signal must be minimized in developing the intensity signal. In order to achieve this end result in the prior art, one or two relatively large surface area photo-diodes separate from the photo-diodes employed for generating the quadrature related fringe signal, are placed in the optical path of the laser beams and their outputs fed to an appropriate amplifier. This, of course, necessitates an additional diode pair beyond the first set of detectors requiring additional wiring, packaging and expense for the fabrication of the unit.